1. Field of the Invention
The present invention relates to an inductance element, and more particularly to an inductance element for use in a microwave integrated circuit for processing high-frequency signals ranging from hundreds of MHz to tens of GHz.
2. Description of the Related Art
Due to the recent rapid development of information networks, a demand for satellite communication systems has remarkably increased with a higher range of frequencies within frequency-band designations often selected. Schottky barrier field effect transistors (MESFETs) using GaAs compound-semiconductors, for instance, have been put into practical use as high-frequency field effect transistors. Moreover, the integration of the initial-stage amplifier unit of a down converter for converting high frequencies to low frequencies (e.g., the application of MMIC: Monolithic Microwave Integrated Circuit) is progressing for the purpose of not only minimizing the system and reducing manufacturing cost but also improving performance of the system.
The reason for applying an MMIC to a communication system that has employed a number of discrete elements is attributed to the fact that circuitry integration makes it possible to decrease the number of parts, thus reducing packaging cost. Consequently, system reliability is improved as the number of connections is decreased and the resulting mass production effect facilitates cost reduction in comparison with a case where a larger number of discrete elements are used for the same purpose.
With such an MMIC, however, it is impossible to fit a coil, formed by axially winding a lead wire, onto the MMIC as an inductance element as such a circuit, being built of a number of discrete elements, is required to be arranged in one plane.
Consequently, a distributed constant line element such as a micro strip line, is employed in the MMIC for use in frequency bands around 10 GHz or over, with desired inductance level by obtained setting the shape, width and the like of the relevant strip line properly. In this case, however, the area occupied by the element tends to increase and this tends to become problematic in MMIC for use at low frequency bands. In MMIC, moreover, the yield rate lowers as the chip size increases, which then becomes detrimental to cost reduction per chip because the relative number of chips obtainable from one sheet of semiconductor substrate decreases.
In order to solve the foregoing problems accompanying the related art system, there has been proposed a so- called spiral inductor in which a conductor line having width of about 2-20 [.mu.m] is formed on a substrate in a spiral manner.
However, such an arrangement, where a conductor line having width of about 2-20 [.mu.m] is arranged spirally, leads to the spiral inductor being substantially square in shape. Although it is advantageous in that the area occupied in this case is smaller than that of an ordinary distributed constant element, it becomes disadvantageous in that the degree of freedom in designing a layout of the circuit on the substrate becomes restricted because of the square shape. When these various kinds of wiring are actually carried out, a dead space develops, thereby resulting in an increase in chip size on the whole, which ultimately affects its yield rate and cost.
Particularly in case of the distributed constant element, the chip size, instead of decreasing, may actually increase with the use of the spiral inductor depending on the desired inductance value and the circuit arrangement, since the degree of freedom in designing the layout is high reduced.